Epa 402-r-93-076 Estimating Radiogenic Cancer Risks

ii The scientific basis for this report has been reviewed formally by the Radiation Advisory Committee (RAC) of the EPA Science Advisory Board (SAB). The following paragraph is a synopsis of that review. (now the Office of Radiation and Indoor Air or ORIA) requested that the RAC review an issues paper comparing health risk estimates due to low level exposures of low-LET radiation based on models recently published by the Committee, provided the Committee's evaluation of the proposed ORIA methodology for estimating radiogenic cancer risks. They concluded that, "Although no single data set and model for predicting radiogenic cancer risk is ideal, the method of analysis chosen by EPA is adequately supported by present evidence." They also offered some comments and suggestions for future consideration. Standards Division, presents radiation risks calculated with the models proposed to the RAC. It also includes risks due to radionuclide intakes and external exposures calculated with those models. ABSTRACT This document presents a revised methodology for EPA's estimation of cancer risks due to low-LET radiation exposures developed in light of information that has become available since the publication of BEIR III, especially new information on the Japanese atomic bomb survivors. For most cancer sites, the risk model is one in which the age-specific relative risk coefficients are obtained by taking the geometric mean of coefficients derived from the atomic bomb survivor data employing two different methods for transporting risks from Japan to the U.S. (multiplicative and NIH projection methods). Using 1980 U.S. vital statistics, the risk models are applied to estimate organ-specific risks, per unit dose, for a stationary population. With the exception of breast cancer, low-LET radiogenic cancer risks are assumed to be reduced by a dose and dose rate effectiveness factor (DDREF) of 2 at low doses and dose rates compared to risks at high acute dose exposure conditions. The DDREF assumed for breast cancer is 1. For low dose (or dose rate) conditions, the calculated risk of a premature cancer death attributable to uniform, whole-body, low-LET irradiation is about 5.1×10 Gy. The corresponding incidence risk (neglecting nonfatal skin cancers) is about-2-1 7.6×10 Gy. High-LET (alpha particle) risks are presumed to increase linearly with dose-2-1 and to be independent of dose rate. Except for leukemia and breast cancer, a relative biological effectiveness (RBE) factor of 20 is adopted for the risk of high-LET radiation relative to that for low-LET radiation at low dose …